Photosensitive materials and compositions containing ionic dye compounds as initiators and thiols as autooxidizers

ABSTRACT

A photohardenable composition comprising a free radical addition polymerizable or crosslinkable compound and an ionic dye-counter ion compound, said compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said compound; and photosensitive materials incorporating the same.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 180,915filed Apr. 13, 1988, now abandoned which in turn is acontinuation-in-part of U.S. patent application Ser. No. 944,305, filedDec. 18, 1986, now U.S. Pat. No. 4,772,530, which in turn is acontinuation-in-part of U.S. patent application Ser. No. 860,367 filedMay 6, 1986, now abandoned which in turn is a continuation-in-part ofU.S. patent application Serial No. 800,014 filed Nov. 20, 1985. nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to novel photohardenable compositions andto photosensitive materials employing them. More particularly, itrelates to free radical addition polymerizable compositions containingan ionic dye-counter ion complex such as a cationic dye-borate anioncomplex or an anionic dye-iodonium ion complex as a photoinitiator.

U.S. Pat. Nos. 4,399,209 and 4,440,846 to The Mead Corporation describeimaging materials and imaging processes in which images are formedthrough exposure controlled release of an image-forming agent from amicrocapsule containing a photohardenable composition. The imagingmaterial is exposed image-wise to actinic radiation and subjected to auniform rupturing force. Typically the image-forming agent is a colorprecursor which is released image-wise from the microcapsules whereuponit reacts with a developer to form a visible image.

One of the problems which has been encountered in designing commerciallyacceptable panchromatic, full color imaging materials employing thesetechniques has been the relatively short wavelengths band to which mostphotohardenable compositions are sensitive to actinic radiation. In mostcases, the compositions are only sensitive to ultraviolet radiation orblue light, e.g., 350 to 480 nm.

Full color photosensitive materials are described in U.S. Pat.Application Ser. No. 339,917, filed Jan. 18, 1982, and U.S. Pat.Application Ser. No. 620,994 filed Jun. 15, 1984. These imagingmaterials include a photosensitive layer which contains three sets ofmicrocapsules. Each set of microcapsules is sensitive to a differentband of radiation in the ultraviolet or blue spectrum and contains acyan, magenta or yellow image-forming agent. The absorption spectra ofthe initiators employed in these microcapsules are never perfectlydistinct. There is always some degree of overlap in the absorptioncurves and sometimes it is substantial. Exposure conditions thereforemust be controlled carefully to avoid cross-exposure.

It would be desirable to extend the sensitivity of the photohardenablecompositions used in these imaging materials to longer wavelengths. Byextending the sensitivity of the photohardenable compositions to longerwavelengths, the amount of overlap in the absorption spectra of theinitiators and the concomitant incidence of cross-exposure can bereduced. It would be particularly desirable if compositions could bedesigned with sensitivities to selected wavelength bands throughout thevisible spectrum (400 to 700 nm) since this would provide a visiblelight-sensitive material which could be exposed by direct reflection ortransmission imaging and without image processing.

SUMMARY OF THE INVENTION

It has been found that ionic dye-counter ion compounds, such as cationicdye-borate anion compounds, are useful photoinitiators of free radicaladdition reactions. Such compounds consist of a visible light absorber(the ionic dye) ionically bonded to a reactive counter ion. The counterion is reactive in the sense that upon excitation of the dye the counterion donates an electron to or accepts an electron from the excited dye.This electron transfer process generates radicals capable of initiatingpolymerization of a monomer.

The mechanism whereby the compounds absorb energy and generate freeradicals is not entirely clear. It is believed that upon exposure toactinic radiation, the dye ion is excited to an excited singlet state inwhich it accepts an electron from or donates an electron to the counterion. For a cationic dye-borate anion compound, this can be illustratedby the following equation:

    BR.sub.4 D.sup.+ →D·+BR.sub.4.

The lifetime of the dye singlet state is extremely short by comparisonto the lifetime of the triplet state. The quenching rate constants whichhave been observed suggest that the ionic compounds experience a veryefficient electron transfer via the singlet state. In solution in thepolymerizable compound, tight ionic pairing of the counter ion and thedye is believed to provide favorable spacial distribution promotingelectron transfer to such an extent that the transfer occurs even thoughthe lifetime of the singlet state is very short. Of course, this doesnot mean that electron transfer is restricted to the singlet state.Ionic dyes which have significant populations of triplet state mayundergo electron transfer through the singlet state, triplet state, orboth singlet and triplet states.

Upon transfer of the electron, a radical is formed. Many of the ioniccompounds used as initiators in the present invention do not appear toexhibit significant back electron transfer. It is believed thatfollowing electron transfer, the dye and counter ion becomedisassociated such that back electron transfer does not occur.

The ionic compounds used in the present invention are different than thecollision generated species encountered in other photosensitive systemssuch as collision complexes which yield encounter complexes, exciplexesand/or contact ion pairs. See for example, Kavarnos, George J. andTurro, Nicholas J., "Photosensitization by Reversible ElectronTransfer", Chem. Rev. 1986, 401-449.

In accordance with the present invention the ionic dye an the counterion are present in the photopolymerizable composition as a stable,non-transient compound, and not as a dissociated ion pair. Formation ofthe compound is not dependent upon diffusion and collision. Asdistinguished from photographic materials and compositions containingcollision dependent complexes essentially all of the sensitizing dyepresent in the photosensitive materials of the present invention priorto exposure is ionically bonded to the counter ion.

The ionic compounds used as initiators in the present invention can alsobe characterized in that they are soluble in nonpolar solvents such asTMPTA and the like. They are soluble in an amount of at least about 0.1%and preferably at least about 0.3% by weight. While these amounts arenot large, they are substantial considering the normally lowersolubility of ionic materials in polar solvents. While the compounds aresoluble, the dye and the counter ion do not dissociate in solution. Theyremain ionically bonded to each other.

In dye-sensitized photopolymerizable compositions, visible light isabsorbed by a dye having a comparable absorption band, the dye is raisedto its excited electronic state, the lifetime of which may be 10⁻⁹ to10⁻³ second, depending upon the nature (singlet or triplet) of theexcited state. During this time, the absorbed energy allows an electronto be transferred to or from the dye molecule to produce the freeradical. In prior initiator systems, this transfer is diffusioncontrolled. The excited dye must interact (collide) with anothermolecule in the composition which quenches the dye and generates a freeradical. In the present invention, the efficiency with which the excitedstate is utilized is not limited by diffusion.

Thus, the present invention provides a means for generating freeradicals from the excited state of an ionic dye and insodoing providesphotohardenable compositions which are sensitive at longer wavelengths.

One of the particular advantages of using ionic dye-counter ioncompounds as initiators of free radical addition reactions is theability to select from a wide variety of dyes which absorb atsubstantially different wavelengths. The absorption characteristics ofthe compound are principally determined by the dye. Thus, by selecting adye which absorbs at 400 nm or greater, the sensitivity of thephotosensitive material can be extended well into the visible range.Furthermore, compounds can be selected which are respectively sensitiveto red, green and blue light without substantial cross-talk.

The ionic dye-counter ion compounds are particularly useful in providingfull color photosensitive materials. In these materials, a layerincluding three sets of microcapsules having distinct sensitivitycharacteristics is provided on a support. Each set of microcapsulesrespectively contains a cyan, magenta, or yellow color-forming agent.

The absorption characteristics of the three sets of microcapsules in afull color photosensitive material must be sufficiently different thatthe cyan-forming capsules can be differentially hardened at apredetermined wavelength or over a predetermined wavelength rangewithout hardening the magenta or yellow-forming capsules and, likewise,the magenta-forming and yellow-forming capsules can be selectivelyhardened upon exposure respectively to second and third wavelengthswithout hardening the cyan-forming capsules or hardening the other ofthe yellow-forming or magenta-forming capsules. Microcapsules havingthis characteristic (i.e., cyan-, magenta- and yellow-forming capsuleswhich can be selectively hardened by exposure at distinct wavelengthswithout cross-exposure) are referred to herein as having "distinctlydifferent sensitivities."

As indicated above, because most photohardenable compositions aresensitive to ultraviolet radiation or blue light and they tend not to besensitive to wavelengths greater than about 480 nm, it has beendifficult to achieve microcapsules having distinct sensitivities atthree wavelengths. Often it can only be achieved by carefully adjustingthe exposure amounts so as not to cross-expose the capsules.

The present invention facilitates the achievement of distinctsensitivities by shifting the peak absorption of at least one of theinitiators to higher wavelengths, such as wavelengths greater than about400 nm. In this manner, instead of attempting to establish distinctsensitivities at three wavelengths within the narrow wavelength rangeof, for example, 350 nm to 480 nm, sensitivity can be established over abroader range of, for example, 350 to 550 nm or higher. In accordancewith the invention, the sensitivity of the microcapsules can be extendedwell into the visible spectrum to 600 nm and in some cases to about 700nm. In the preferred case compounds are provided which are respectivelysensitive to red, green and blue light.

In addition to use of the photoinitiators or providing full colorphotosensitive materials, other uses are envisioned. For example, it iscontemplated that the photoinitiators may be used in connection withlight curable dental adhesives, as sensitizers for photopolymerholography, in light curable coatings containing ultraviolet-absorbersfor photostabilization, in three-dimensional model formation and inapplying underwater coatings.

A principal object of the present invention is to providephotohardenable compositions which are sensitive to visible light, e.g.,wavelengths greater than about 400 nm.

A further object of the present invention is to provide visiblelight-sensitive photohardenable compositions which are useful in theimaging materials described in U.S. Pats. Nos. 4,399,209 and 4,440,846.

Another object of the present invention is to provide photohardenablecompositions which are sensitive at greater than about 400 nm and whichare useful as photoresists or in forming polymer images.

These and other objects are accomplished in accordance with the presentinvention which, in one embodiment, provides:

A photohardenable composition comprising a free radical additionpolymerizable or crosslinkable compound and a ionic dye-reactive counterion compound, said ionic dye-reactive counter ion compound being capableof absorbing actinic radiation and producing free radicals whichinitiate free radical addition polymerization or crosslinking of saidaddition polymerizable or crosslinkable compound.

Another embodiment of the present invention resides in a photosensitivematerial comprising a support having a layer of photosensitivemicrocapsules on the surface thereof, said microcapsules containing aninternal phase including a photohardenable composition comprising a freeradical addition polymerizable or crosslinkable compound and an ionicdye-reactive counter ion compound.

Still another embodiment of the present invention resides in aphotosensitive material useful in forming full color images comprising asupport having a layer of photosensitive microcapsules on the surfacethereof, said photosensitive microcapsules comprising a first set ofmicrocapsules having a cyan image-forming agent associated therewith, asecond set of microcapsules having a magenta image-forming agentassociated therewith, and a third set of microcapsules having a yellowimage-forming agent associated therewith, at least one of said first,second, and third sets of microcapsules containing an internal phasewhich includes a photohardenable composition including a free radicaladdition polymerizable or crosslinkable compound and an ionicdye-reactive counter ion compound.

A further embodiment of the present invention resides in aphotosensitive material comprising a support having a layer of aphotohardenable composition on the surface thereof, said photohardenablecomposition comprising a free radical addition polymerizable orcrosslinkable compound and an ionic dye-reactive counter ion compoundwhich provides a quenching constant (Kq) which is greater than 10¹⁰ andpreferably greater than 10¹².

In accordance with more particular embodiments of the invention, theionic compound is a cationic dye-borate anion compound and still moreparticularly a cyanine dyeborate anion compound; or an anionic dyecompound such as ionic compounds of xanthene dyes with iodonium orpyryllium ions.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Pats. Nos. 4,399,209 and 4,440,846 and U.S. Pat. Applications Ser.No. 339,917, filed Jan. 18, 1982, and U.S. Pat. Ser. No. 620,994, filedJun. 15, 1984, are incorporated herein by reference to the extent thatreference thereto may be necessary to complete this disclosure.

Cationic dye-borate anion compounds are known in the art. Theirpreparation and use in imaging systems is described in U.S. Pats. Nos.3,567,453; 4,307,182; 4,343,891; 4,447,521; and 4,450,227. The compoundsused in the present invention can be represented by the general formula(I): ##STR1## where D⁺ is a cationic dye; and R¹, R², R³, and R⁴ areindependently selected from the group consisting of alkyl, aryl,alkaryl, allyl, aralkyl, alkenyl, alkynyl, alicyclic and saturated orunsaturated heterocyclic groups.

Useful dyes form photoreducible but dark stable complexes with borateanions and can be cationic methine, polymethine, triarylmethane,indoline, thiazine, xanthene, oxazine and acridine dyes. Morespecifically, the dyes may be cationic cyanine, carbocyanine,hemicyanine, rhodamine and azomethine dyes. In addition to beingcationic, the dyes should not contain groups which would neutralize ordesensitize the complex or render the complex poorly dark stable.Examples of groups which generally should not be present in the dye areacid groups such as free carboxylic or sulphonic acid groups.

Specific examples of useful cationic dyes are Methylene Blue, Safranine0, Malachite Green, cyanine dyes of the general formula (II) andrhodamine dyes of the formula (III): ##STR2## n=0, 1, 2, 3 R=alkyl

Y═CH═CH, N--CH₃, C(CH₃)₂, O, S, Se ##STR3## R', R=alkyl, aryl, and anycombination thereof

While they have not been tested, the cationic cyanine dyes disclosed inU.S. Pat. No. 3,495,987 should be useful in the present invention.

The borate anion is designed such that the borate radical generated uponexposure to light and after electron transfer to the dye (Eq. 1) readilydissociates with the formation of a radical as follows:

    BR.sub.4 ·→BR.sub.3 +R·           (Eq. 2)

For example particularly preferred anions are triphenylbutylborate andtrianisylbutylborate anions because they readily dissociate totriphenylborane or trianisylborane and a butyl radical. On the otherhand tetrabutylborate anion does not work well presumably because thetetrabutylborate radical is not stable and it readily accepts anelectron back from the dye in a back electron transfer and does notdissociate efficiently. Likewise, tetraphenylborate anion is very poorbecause the phenyl radical is not easily formed.

Preferably, at least one but not more than three of R¹ R², R³, and R⁴ isan alkyl group. Each of R¹, R², R³, and R⁴ can contain up to 20 carbonatoms, and they typically contain 1 to 7 carbon atoms. More preferablyR¹ -R⁴ are a combination of alkyl group(s) and aryl group(s) or aralkylgroup(s) and still more preferably a combination of three aryl groupsand one alkyl group.

Representative examples of alkyl groups represented by R¹ -R⁴ aremethyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, stearyl, etc. Thealkyl groups may be substituted, for example, by one or more halogen,cyano, acyloxy, acyl, alkoxy or hydroxy groups.

Representative examples of aryl groups represented by R¹ -R⁴ includephenyl, naphthyl and substituted aryl groups such as anisyl. Alkarylgroups include methylphenyl, dimethylphenyl, etc. Representativeexamples of aralkyl groups represented by R¹ -R⁴ groups include benzyl.Representative alicyclic groups include cyclobutyl, cyclopentyl, andcyclohexyl groups. Examples of an alkynyl group are propynyl andethynyl, and examples of alkenyl groups include a vinyl group.

As a general rule, useful ionic dye compounds must be identifiedempirically, however, potentially useful dye and counter ioncombinations can be identified by reference to the Weller equation(Rehm, D. and Weller, A., Isr. J Chem. (1970), 8, 259-271), which can besimplified as follows.

    ΔG=E.sub.ox -E.sub.red -E.sub.h ν                 (Eq. 3)

where ΔG is the change in the Gibbs free energy, E_(ox) is the oxidationpotential of the borate anion BR-₄, E_(red) is the reduction potentialof the cationic dye, and E_(h)ν is the energy of light used to excitethe dye. Useful compounds will have a negative free energy change.Similarly, the difference between the reduction potential of the dye andthe oxidation potential of the borate must be positive for the compoundsto be dark stable, i.e., Eox - Ered>0.

As indicated, Eq. 2 is a simplification and it does not absolutelypredict whether a compound will be useful in the present invention ornot. There are a number of other factors which will influence thisdetermination. One such factor is the effect of the monomer on thecompound. Another factor is the radial distance between the ions. It isalso known that if the Weller equation produces too negative a value,deviations from the equation are possible. Furthermore, the Wellerequation only predicts electron transfer, it does not predict whether aparticular compound is an efficient initiator of polymerization. Theequation is a useful first approximation.

Specific examples of cationic dye-borate anion compounds useful in thepresent invention are shown in the following table with their λ max.

                                      TABLE                                       __________________________________________________________________________    Compound No.                                                                          Structure                          λmax (TMPTA)                __________________________________________________________________________             ##STR4##                          552 nm                                      ##STR5##                          568 nm                                      ##STR6##                          492 nm                                      ##STR7##                          428 nm                                      ##STR8##                          658 nm                                      ##STR9##                          528 nm                                      ##STR10##                         450 nm                                       No.          R'             Ar                                                7A           n-butyl        phenyl                                            7B           n-hexyl        phenyl                                            7C           n-butyl        anisyl                                           ##STR11##                         550 nm                                    No.       R'           R          Ar                                          8A        methyl       n-butyl    phenyl                                      8B        methyl       n-hexyl    phenyl                                      8C        n-butyl      n-buytl    phenyl                                      8D        n-butyl      n-hexyl    phenyl                                      8E        n-heptyl     n-butyl    phenyl                                      8F        n-heptyl     n-hexyl    phenyl                                      8G        ethyl        n-butyl    phenyl                                        ##STR12##                         570 nm System                      10.                                                                                    ##STR13##                         590 nm System                               ##STR14##                         640 nm                                    No.       R            R'         Ar                                          11A       methyl       n-butyl    phenyl                                      11B       methyl       n-hexyl    phenyl                                      11C       n-butyl      n-butyl    phenyl                                      11D       n-butyl      n-hexyl    phenyl                                      11E       n-pentyl     n-butyl    phenyl                                      11F       n-pentyl     n-hexyl    phenyl                                      11G       n-heptyl     n-butyl    phenyl                                      11H       n-heptyl     n-hexyl    phenyl                                      11I       methyl       n-butyl    anisyl                                        ##STR15##                         740 nm System                               ##STR16##                         462 nm                                            AR                R                                                           phenyl            n-butyl                                      __________________________________________________________________________

The cationic dye-borate anion compounds can be prepared by reacting aborate salt with a dye in a counterion exchange in a known manner. SeeHishiki, Y., Repts. Sci. Research Inst. (1953), 29, pp 72-79. Usefulborate salts are sodium salts such as sodium tetraphenylborate, sodiumtriphenylbutylborate, sodium trianisylbutylborate and ammonium saltssuch as tetraethylammonium tetraphenylborate.

Anionic dye compounds are also useful in the present invention. Anionicdye-iodonium ion compounds of the formula (IV):

    [R.sup.5 --I.sup.⊕ --R.sup.6 ]n.sup.D-n                (IV)

where D⁻ is an anionic dye and R⁵ and R⁶ are independently selected fromthe group consisting of aromatic nuclei such as phenyl or naphthyl and nis 1 or 2; and anionic dye-pyryllium compounds of the formula (V):##STR17## where D⁻ and n are as defined above are typical examples ofanionic dye complexes.

Representative examples of anionic dyes include xanthene and oxonoldyes. For example Rose Bengal, eosin, erythiosin, and fluorscein dyesare useful. In addition to iodonium and pyryllium ions, other compoundsof anionic dyes and sulfonium and phosphonium cations are potentiallyuseful.

As in the case of the cationic dye compounds, useful dye-cationcombinations can be identified through the Weller equation as having anegative free energy.

Selected examples of anionic dye compounds are shown in Table 2 (λ max.ca. 570 nm in TMPTA). In Table 2 the symbol φ is used for a phenyl groupand the structure ##STR18## is used for ##STR19##

                  TABLE 2                                                         ______________________________________                                                           (φ.sub.2 I.sup.+).sub.2                                 ##STR20##                                                                                        ##STR21##                                                  ##STR22##                                                                                        ##STR23##                                                  ##STR24##                                                                                        ##STR25##                                                  ##STR26##                                                                                        ##STR27##                                                  ##STR28##         φ.sub.2 I.sup.+                                         ##STR29##                                                                                        ##STR30##                                                  ##STR31##         φ.sub.3.sup.+PCH.sub.2 φ                            ##STR32##         CH.sub.3.sup.+Sφ .sub.2                                 ##STR33##                                                                                        ##STR34##                                                  ##STR35##         φ.sub.2 I.sup.+                                        ______________________________________                                    

The most typical examples of a free radical addition polymerizable orcrosslinkable compound useful in the present invention is anethylenically unsaturated compound and, more specifically, apolyethylenically unsaturated compound. These compounds include bothmonomers having one or more ethylenically unsaturated groups, such asvinyl or allyl groups, and polymers having terminal or pendant ethylenicunsaturation. Such compounds are well known in the art and includeacrylic and methacrylic esters of polyhydric alcohols such astrimethylolpropane, pentaerythritol, and the like; and acrylate ormethacrylate terminated epoxy resins, acrylate or methacrylateterminated polyesters, etc. Representative examples include ethyleneglycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropanetriacrylate (TMPTA), pentaerythritol tetraacrylate, pentaerythritoltetramethacrylate, dipentaerythritol hydroxypentacrylate (DPHPA),hexanediol-1,6-dimethacrylate, and diethyleneglycol dimethacrylate.

The ionic dye compound is usually used in an amount up to about 1% byweight based on the weight of the photopolymerizable or crosslinkablespecies in the photohardenable composition. More typically, the compoundis used in an amount of about 0.2% to 0.5% by weight.

While the compound can be used alone as the initiator, film speeds tendto be quite slow and oxygen inhibition is observed. It has been foundthat it is preferable to use the compound in combination with anautoxidizer. An autoxidizer is a compound which is capable of consumingoxygen in a free radical chain process.

Examples of useful autoxidizers are N,N-dialkylanilines. Examples ofpreferred N,N-dialkylanilines are dialkylanilines substituted in one ormore of the ortho-, meta-, or para- position by the following groups:methyl, ethyl, isopropyl, t-butyl, 3,4-tetramethylene, phenyl,trifluoromethyl, acetyl, ethoxycarbonyl, carboxy, carboxylate,trimethylsilymethyl, trimethylsilyl, triethylsilyl, trimethylgermanyl,triethylgermanyl, trimethylstannyl, triethylstannyl, n-butoxy,n-pentyloxy, phenoxy, hydroxy, acetyl-oxy, methylthio, ethylthio,isopropylthio, thio-(mercapto-), acetylthio, fluoro, chloro, bromo andiodo.

Representative examples of N,N-dialkylanilines useful in the presentinvention are 4-cyano-N,N-dimethylaniline, 4-acetyl-N,N-dimethylaniline,4-bromo-N,N-dimethylaniline, ethyl 4-(N,N-dimethylamino) benzoate,3-chloro-N,N-dimethylaniline, 4-chloro-N,N-dimethylaniline,3-ethoxy-N,N-dimethylaniline, 4-fluoro-N,N-dimethylaniline,4-methyl-N,N-dimethylaniline, 4-ethoxy-N,N-dimethylaniline,N,N-dimethylthioanicidine, 4-amino-N,N-dimethylaniline,3-hydroxy-N,N-dimethylaniline, N,N,N', N'-tetramethyl-1,4-dianiline,1,4-dianiline, 4-acetamido-N,N-dimethylaniline, etc.

Preferred N,N-dialkylanilines are substituted with an alkyl group in theortho-position and include 2,6-diisopropyl-N,N-dimethylaniline,2,6-diethyl-N,N-dimethylaniline, N,N,2,4,6-pentamethylaniline (PMA) andp-t-butyl-N,N-dimethylaniline.

Another useful class of autooxidizer is thiols such asmercaptobenzoxazoles, mercaptotetrazines, and mercaptotriazines.Specific examples of useful thiols include: 2-mercaptobenzothiazole,6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzoxazole,4-methyl-4H-1,2,4-triazole-3-thiol, 2-mercapto-1-methylimidazole,2-mercapto-5-methylthio-1,3,4-thiadiazole,5-n-butylthio-2-mercapto-1,3,4-thiadiazole, 4-methoxybenzenethiol,1-phenyl-1H-tetrazole-5-thiol, 4-phenyl-4H-1,2,4-triazole-3-thiol,2-mercaptobenzimidazole, pentaerythritol tetrakis(mercaptoacetate),pentaerythritol tetrakis(3-mercaptoproprionate), trimethylolpropane tris(mercapto-acetate), trimethylolpropane tris(3-mercaptopropionate),4-acetamidothiophenol, mercaptosuccinic acid, dodecanethiol,2-mercaptopyridine, 4-mercaptopyridine, 2-mercapto-3H-quinazoline, and2-mercaptothiazoline.

The autoxidizers are preferably used in the present invention inconcentrations of about 4-5% by weight.

In some cases, the ionic dye compounds generate radicals upon heating,i.e., they behave as thermal initiators. This can cause thephotosensitive composition to harden during storage at elevatedtemperatures which, in turn, detracts from the shelf life of the imagingsystem. To prevent thermal initiation and improve shelf life, it isdesirable to include a thermal polymerization inhibitor in the internalphase. Where the dye is oxidized in the course of initiation, thethermal polymerization inhibitor is an antioxidant such as2,6-di-tert-butyl-4-methylphenol. Other useful thermal polymerizationinhibitors are known and can also be used to improve shelf life.

The photohardenable compositions of the present invention can be coatedupon a support in a conventional manner and used as a photoresist or inphotolithography to form a polymer image; or they can be encapsulated asdescribed in U.S. Pat. Nos. 4,399,209 and 4,440,846 and used to controlthe release of an image-forming agent. The latter processes typicallyinvolve image-wise exposing the photosensitive material to actinicradiation and subjecting the layer of microcapsules to a uniformrupturing force such as pressure, abrasion, or ultrasonic energywhereupon the image-forming agent is released from the microcapsules forreaction with a developer.

Several processes can be used to form color images as explained in U.S.Pat. Application Ser. No. 339,917. If the microcapsules containphotosensitive compositions which are sensitive to red, green and bluelight, images can be formed by direct transmission or reflection imagingor by image processing. Image processing may involve forming colorseparations (color-seps) corresponding to the red, green and bluecomponent images and sequentially exposing the photosensitive materialto three distinct bands of radiation hereinafter designated λ-1, λ-2,and λ-3 through each color separation. Otherwise, it may involveelectronic processing in which the image or subject to be recorded isviewed through a Dunn or matrix camera and the output from the cameraelectronically drives three exposure sources corresponding to λ-1, λ-2,and λ-3. Alternatively, the image may be produced synthetically, e.g., acomputer-generated image.

While the discussion herein relates to forming 3-color full colorimages, 4-color images are also possible. For example, microcapsulescontaining cyan, magneta, yellow, and black image-forming agents can beprovided which have distinct sensitivities at four wavelengths, e.g.,λ-1, λ-2, λ-3, and λ-4.

In accordance with the invention, at least one set of the microcapsulesin a full color system contains an ionic dye compound. The other setsalso may contain an ionic dye compound, or they may contain a differenttype of photoinitiator.

In accordance with the preferred embodiments of the invention, a fullcolor imaging system is provided in which the microcapsules aresensitive to red, green, and blue light respectively. The photosensitivecomposition in at least one and possibly all three microcapsules aresensitized by an ionic dye compound. For optimum color balance, themicrocapsules are sensitive (λmax) at about 450 nm, 550 nm, and 650 nm,respectively. Such a system is useful with visible light sources indirect transmission or reflection imaging. Such a material is useful inmaking contact prints or projected prints of color photographic slides.They are also useful in electronic imaging using lasers or pencil lightsources of appropriate wavelengths.

Because the ionic dye compounds absorb at wavelengths greater than 400nm, they are colored. Typically, the unexposed dye compound is presentwith the image-forming agent in the image areas and, thus, the color ofthe compound must be considered in determining the color of the image.However, the compound is used in very small amounts compared to theimage-forming agent and exposure sometimes bleaches the compound.

The photohardenable compositions of the present invention can beencapsulated in various wall formers using techniques known in the areaof carbonless paper including coacervation, interfacial polymerization,polymerization of one or more monomers in an oil, as well as variousmelting, dispersing, and cooling methods. To achieve maximumsensitivities, it is important that an encapsulation technique be usedwhich provides high quality capsules which are responsive to changes inthe internal phase viscosity in terms of their ability to rupture.Because the borate tends to be acid sensitive, encapsulation proceduresconducted at higher pH (e.g., greater than about 6) are preferred.

Oil soluble materials have been encapsulated in hydrophilic wall-formingmaterials such as gelatin-type materials (see U.S. Pat. Nos. 2,730,456and 2,800,457 to Green et al) including gum arabic, polyvinyl alcohol,carboxy-methylcellulose; resorcinol-formaldehyde wall formers (see U.S.Pat. No. 3,755,190 to Hart, et al); isocyanate wall-formers (see U.S.Pat. No. 3,914,511 to Vassiliades); isocyanate-polyol wall-formers (seeU.S. Pat. No. 3,796,669 to Kiritani et al); urea-formaldehydewall-formers, particularly urea-resorcinol-formaldehyde in whicholeophilicity is enhanced by the addition of resorcinol (see U.S. Pat.Nos. 4,001,140; 4,087,376 and 4,089,802 to Foris et al);melamine-formaldehyde resin and hydroxypropyl cellulose (see commonlyassigned U.S. Pat. No. 4,025,455 to Shackle); and UF capsules formedusing pectin as a system modifier as discussed in U.S. Pat. No.4,608,330 to Marabella.

Urea-resorcinol-formaldehyde and melamine-formaldehyde capsules with lowoxygen permeability are preferred. In some cases to reduce oxygenpermeability it is desirable to form a double walled capsule byconducting encapsulation in two stages.

A capsule size should be selected which minimizes light attenuation. Themean diameter of the capsules used in this invention typically rangesfrom approximately 1 to 25 microns. As a general rule, image resolutionimproves as the capsule size decreases. If the capsules become toosmall, they may become inaccessible in the pores or the fiber of thesubstrate. These very small capsules may therefore be screened fromexposure by the substrate. They may also fail to rupture when exposed topressure or other rupturing means. In view of these problems, it hasbeen determined that a preferred mean capsule diameter range is fromapproximately 10 microns. Technically, however, the capsules can rangein size up to the point where they become visible to the human eye.

An open phase system may also be used in accordance with the inventioninstead of an encapsulated one. This can be done by dispersing whatwould otherwise be the capsule contents throughout the coating on thesubstrate as discrete droplets. Suitable coatings for this embodimentinclude polymer binders whose viscosity has been adjusted to match thedispersion required in the coating. Suitable binders are gelatin,polyvinyl alcohol, polyacrylamide, and acrylic lattices. Wheneverreference is made to "capsules" and "encapsulation" without reference toa discrete capsule wall in this specification or the appended claims,those terms are intended to include the alternative of an open phasesystem.

The photosensitive material of the present invention can be used tocontrol the interaction of various image-forming agents.

In one embodiment of the present invention the capsules may contain abenign visible dye in the internal phase in which case images are formedby contacting the exposed imaging material under pressure with a plainpaper or a paper treated to enhance its affinity for the visible dye. Abenign dye is a colored dye which does not interfere with the imagingphotochemistry, for example, by relaxing the excited state of theinitiator or detrimentally absorbing or attenuating the exposureradiation.

In a preferred embodiment of the invention, images are formed throughthe reaction of a pair of chromogenic materials such as a colorprecursor and a color developer, either of which may be encapsulatedwith the photohardenable composition and function as the image formingagent. In general, these materials include colorless electron donatingtype compounds and are well known in the art. Representative examples ofsuch color formers include substantially colorless compounds having intheir partial skeleton a lactone, a lactam, a sultone, a spiropyran, anester or an amido structure such as triarylmethane compounds,bisphenylmethane compounds, xanthene compounds, fluorans, thiazinecompounds, spiropyran compounds and the like. Crystal Violet Lactone andCopiken X, IV and XI are often used. The color formers can be used aloneor in combination.

The developer materials conventionally employed in carbonless papertechnology are also useful in the present invention. Illustrativeexamples are clay minerals such as acid clay, active clay, attapulgite,etc.; organic acids such as tannic acid, gallic acid, propyl gallate,etc.; acid polymers such as phenol-formaldehyde resins, phenol acetylenecondensation resins, condensates between an organic carboxylic acidhaving at least one hydroxy group and formaldehyde, etc.; metal salts oraromatic carboxylic acids such as zinc salicylate, tin salicylate, zinc2-hydroxy naphthoate, zinc 3,5 di-tert butyl salicylate, zinc3,5-di-(α-methylbenzyl)salicylate, oil soluble metal salts orphenol-formaldehyde novolak resins (e.g., see U.S. Pat. Nos. 3,672,935;3,732,120 and 3,737,410) such as zinc modified oil solublephenol-formaldehyde resin as disclosed in U.S. Pat. No. 3,732,120, zinccarbonate etc. and mixtures thereof.

As indicated in U.S. Pat. No. 4,399,209 and 4,440,846, the developer maybe present on the photosensitive sheet (providing a so-calledself-contained system) or on a separate developer sheet.

In self-contained systems, the developer may be provided in a singlelayer underlying the microcapsules as disclosed in U.S. Pat. No.4,440,846. Alternatively, the color former and the color developer maybe individually encapsulated in photosensitive capsules and uponexposure both capsule sets image-wise rupture releasing color former anddeveloper which mix to form the image. Alternatively, the developer canbe encapsulated in non-photosensitive capsules such that upon processingall developer capsules rupture and release developer but the colorformer containing capsules rupture in only the unexposed or underexposedarea which are the only areas where the color former and developer mix.Still another alternative is to encapsulate the developer inphotosensitive capsules and the color former in non-photosensitivecapsules.

The present invention is not necessarily limited to embodiments wherethe image-forming agent is present in the internal phase. Rather, thisagent may be present in the capsule wall of a discrete capsule or in thebinder of an open phase system or in a binder or coating used incombination with discrete capsules or an open phase system designed suchthat the image-wise ruptured capsules release a solvent for theimage-forming agent. Embodiments are also envisioned in which a dye orchromogenic material is fixed in a capsule wall or binder and isreleased by interaction with the internal phase upon rupturing thecapsules.

The most common substrate for this invention is a transparent film sinceit assists in obtaining uniform development characteristics, however,paper may also be used. The paper may be a commercial impact raw stock,or special grade paper such as cast-coated paper or chrome-rolled paper.Transparent films such as polyethylene terephthalate can be used.Translucent substrates can also be used in this invention.

Synthesis Examples 1 and 2 respectively illustrate the preparation ofborates and dye-borate compounds.

SYNTHESIS EXAMPLE 1

Dissolve triphenylborane in 150 ml dry benzene (1M) under nitrogenatmosphere. Place flask in a cool water bath and, while stirring, addn-BuLi, (1.1 e.g.) via syringe. A white precipitate soon formed afteraddition was started. Stirring is continued about 45-60 min. Dilute with100 ml hexane and filter, washing with hexane. This resultant Li salt isslightly air unstable. Dissolve the white powder in about 200 mldistilled water and, with vigorous stirring, add aqueous solution oftetramethyl ammonium chloride (1.2 e.g. of theoretical in 200 ml). Athick white precipitate forms. Stir this aqueous mixture about 30 min.at room temperature, then filter. Wash collected white solid withdistilled water.

As an alternative synthesis, to a 1.0M solution of 2.0 equivalents of1-butene in dry, oxygen-free dichloromethane, under inert atmosphere,was added slowly dropwise with stirring, 1.0 equivalents of a 1.0Msolution of dibromethane-methylsulfide complex in dichloromethane. Thereaction mixture stirred at reflux for 36 hours and the dichloromethaneand excess 1-butene were removed by simple distillation. Vacuumdistillation of the residue afforded 0.95 equivalents of a colorlessmobile oil (Bp 66-7 0.35 mm Hg, ¹¹ BNMR;bs (4.83PPM)). Under inertatmosphere, this oil was dissolved in dry, oxygen-free tetrahydrofuranto give a 1.0M solution and 3.0 equivalents of a 2.0M solution ofphenylmagnesium chloride in tetrahydrofuran were added dropwise withstirring. After stirring 16 hours, the resultant solution was addedslowly with vigorous stirring to 2 equivalents of tetramethylammoniumchloride, as a 0.2M solution, in water. The resulting white flocculatesolid was filtered and derived to afford a near quantitative amount ofthe desired product Mp 250-2° C., ¹¹ BNMR;bs (-3.70PPM).

SYNTHESIS EXAMPLE 2

Sonicate a suspension of a borate salt (1 g/10 ml) in MeOH, to make avery fine suspension. Protect flask from light by wrapping with aluminumfoil then add 1 equivalent of dye. Stir this solution with low heat on ahot plate for about 30 min. Let cool to room temperature then dilutewith 5-10 volumes of ice water. Filter the resultant solid and wash withwater until washings are colorless. Suction filter to dryness.Completely dry initiator compound by low heat (about 50° C.) in a vacuumdrying oven. Initiator is usually formed quantitatively. Analysis byH-NMR indicates 1:1 compound formation typically greater than 90%.

SYNTHESIS EXAMPLE 3

30 millimoles of neutral acriflavine was dissolved in 200 mls of hot CH₃OH. To this solution was added 30 millimoles of solidtetramethylammonium n-butyltriphenyl borate stirred in 100 mls of CH₃OH. To this resulting mixture was added 50 mls of acetone. The reactionsolution was heated overnight and was filtered. The filtrate was treatedwith 500 mls of ice-water to produce 3.10 grams of acriflavinen-butyltriphenyl borate. This compound was dissolved in TMPTA at roomtemperature to give a yellow solution having a concentration of7.05×10⁻⁶ M. A drop of this solution was placed between two microscopeslides and the slides were exposed to visible light. The microscopeslides locked up demonstrating that the TMPTA had polymerized.

The present invention is illustrated in more detail by the followingnon-limiting Examples.

EXAMPLE 1 Capsule Preparation

1. Into a 600 ml stainless steel beaker, 104 g water and 24.8 gisobutylene maleic anhydride copolymer (18%) are weighed.

2. The beaker is clamped in place on a hot plate under an overheadmixer. A six-bladed, 45° pitch, turbine impeller is used on the mixer.

3. After thoroughly mixing, 3.1 pectin (polygalacturonic acid methylester) is slowly sifted into the beaker. This mixture is stirred for 20minutes.

4. The pH is adjusted to 4.0 using a 20% solution of H₂ SO₄, and 0.1 gQuadrol (2-hydroxypropyl ethylenediamine with propylene oxide from BASF)is added.

5. The mixer is turned up to 3000 rpm and the internal phase is addedover a period of 10-15 seconds. Emulsification is continued for 10minutes.

6. At the start of emulsification, the hot plate is turned up so heatingcontinues during emulsification.

7. After 10 minutes, the mixing speed is reduced to 2000 rpm and 14.1 gurea solution (50% w/w), 3.2 g resorcinol in 5 g water, 21.4 gformaldehyde (37%), and 0.6 g ammonium sulfate in 10 ml water are addedat two-minute intervals.

8 The beaker is covered with foil and a heat gun is used to help bringthe temperature of the preparation to 65° C. When 65° C. is reached, thehot plate is adjusted to maintain this temperature for a two to threehour cure time during which the capsule walls are formed.

9. After curing, the heat is turned off and the pH is adjusted to 9.0using a 20% NaOH solution.

10. Dry sodium bisulfite (2.8 g) is added and the capsule preparation iscooled to room temperature.

Three batches of microcapsules were prepared for use in a full colorimaging sheet using the three internal phase compositions set forthbelow. Internal Phase A provides a yellow image-forming agent and issensitive at 420 nm, Phase B provides a magenta image-forging agent andis sensitive at 480 nm, and Phase C contains a cyan image-forming agentand cationic dye-borate anion complex which is sensitive at 570 nm. Thethree batches of microcapsules were mixed, coated on a support, anddried to provide a full color imaging sheet.

    ______________________________________                                        Internal Phase A (420 nm)                                                     TMPTA                      35 g                                               DPHPA                      15 g                                               3-Thenoyl-7-diethylamino coumarin                                                                        15 g                                               2-Mercaptobenzoxazole (MBO)                                                                              2.0 g                                              Pentamethylaniline (PMA)   1.0 g                                              Reakt Yellow (BASF)        5.0 g                                              SF-50 (Union Carbide Isocyanate)                                                                         1.67 g                                             N-100 (Desmodur Polyisocyanate Resin)                                                                    3.33 g                                             Internal Phase B (480 nm)                                                     TMPTA                      35 g                                               DPHPA                      15 g                                               9-(4'-Isopropylcinnamoyl)- 0.15 g                                             1,2,4-tetrahydro-3H, 6H, 10H[1]-                                              benzopyrano[9, 9A,1-yl]quinolazine-                                           10-one                                                                        MBO                        1.0 g                                              PMA                        2.0 g                                              Magenta Color Former       8.0 g                                              (HD-5100 Hilton Davis Chemical Co.)                                           SF-50                      1.67 g                                             N-100                      3.33 g                                             Internal Phase C (570 nm)                                                     TMPTA                      50. g                                              Cationic Dye Compound No. 2                                                                              0.15 g                                             PMA                        2.00 g                                             Cyan Color Former          4.0 g                                              (S-29663 Hilton Davis Chemical Co.)                                           SF-50                      1.67 g                                             N-100                      3.33 g                                             ______________________________________                                    

EXAMPLE 2 Capsule Preparation

1. Into a 600 ml stainless steel beaker, 110 g water and 4.6 gisobutylene maleic anhydride copolymer (dry) are weighed.

2. The beaker is clamped in place on a hot plate under an overheadmixer. A six-bladed, 45° pitch, turbine impeller is used on the mixer.

3. After thoroughly mixing, 4.0 g pectin (polygalacturonic acid methylester) is slowly sifted into the beaker. The mixture is stirred for 2hours at room temperature (800-1200 rmp).

4. The pH is adjusted to 7.0 with 20% sulfuric acid.

5. The mixer is turned up to 3000 rpm and the internal phase is addedover a period of 10-15 seconds. Emulsification is continued for 10minutes. Magenta and yellow precursor phases are emulsified at 25-30° C.Cyan phase is emulsified at 45-50° C. (oil), 25-30° C. (water).

6. At the start of emulsification, the hot plate is turned up so heatingcontinues during emulsification.

7. After 10 minutes, the pH is adjusted to 8.25 with 20% sodiumcarbonate, the mixing speed is reduced to 2000 rpm, and a solution ofmelamine-formaldehyde prepolymer is slowly added which is prepared bydispersing 3.9 g melamine in 44 g water, adding 6.5 g formaldehydesolution (37%) and heating at 60° C. until the solution clears plus 30minutes.

8. The pH is adjusted to 6.0, the beaker is covered with foil and placedin a water bath to bring the temperature of the preparation to 65° C.When 65° C. is reached, the hot plate is adjusted to maintain thistemperature for a two hour cure time during which the capsule walls areformed.

9. After curing, mixing speed is reduced to 600 rpm, formaldehydescavenger solution (7.7 g urea and 7.0 g water) is added and thesolution was cured another 40 minutes.

10. The pH is adjusted to 9.5 using a 20% NaOH solution and stirredovernight at room temperature.

Three batches of microcapsules were prepared as above for use in a fullcolor imaging sheet using the three internal phase compositions setforth below.

    ______________________________________                                        Yellow Forming Capsules (420 nm)                                              TMPTA                      35 g                                               DPHPA                      15 g                                               3-Thenoyl-7-diethylamino coumarin                                                                        15 g                                               2-Mercaptobenzoxazole (MBO)                                                                              2.0 g                                              2,6-Diisopropylaniline     1.0 g                                              Reakt Yellow (BASF)        5.0 g                                              N-100 (Desmodur Polyisocyanate Resin)                                                                    3.33 g                                             Magenta Forming Capsules (550 nm)                                             TMPTA                      50 g                                               Compound 8A                0.2 g                                              2,6-Diisopropylaniline     2.0 g                                              HD5100 (Magenta color      12.0 g                                             precursor from Hilton-Davis                                                   Chemical Co.)                                                                 Cyan Forming Capsules (650 nm)                                                TMPTA                      50 g                                               Compound 11 H              0.31 g                                             2,6-diisopropylaniline     2.0 g                                              Cyan Precursor (CP-177     6 g                                                of Hilton-Davis Chemical Co.)                                                 ______________________________________                                    

The three batches of microcapsules were blended together and coated on asupport to provide an imaging material in accordance with the presentinvention.

The inventive compositions of the present invention may be used inconnection with dental adhesives and compositions. Many commerciallyused adhesives are based upon photopolymerizable acrylate polymers. Forexample, commonly used adhesives are based upon bis-GMA(2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]-propane, sometimesreferred to as diglycidyl methacrylate of bisphenol A. Representativesof such compounds are set forth in U.S. Pat. Nos. 4,089,763; 4,459,193;4,479,782; 4,490,115; 4,491,453; 4,515,930; 4,553,940; and at pages501-508 and 515-517 of the Kirk-Othmer Encyclopedia of ChemicalTechnology, Third Edition, Volume 7 (1979). These compounds require aphotoinitiator and may also include an amount of an inert dental fillermaterial. Examples of dental filler materials include natural materialssuch as quartz, feldstone, pottery stone, wallastonite, mica, clay,kaolin, and marble; ceramics such as silica, aluminum, silicon nitride,boron carbide, boron nitride, soda glass, barium glass, strontium glass,borosilicate glass, and lanthanum-containing glass ceramic; andwater-insoluble inorganic salts such as barium sulfate and calciumcarbonate. The preferred photoinitiators were usually based upon alphadiketones. These initiators are disadvantageous as they are low inefficiency and absorptivity. Further, it is necessary to use eitherultraviolet or blue light to initiate photopolymerization.

In accordance with the present invention, instead of using an alphadiketone initiator the inventive ionic dye-counter ion complexes areused as photoinitiators. Preferred photoinitiators are the cationicdye-borate anion complexes. Use of these initiators enables lightemitted from a broad band visible light source to photoadhere dentalwork to teeth. Thus, the requirement of using harmful ultraviolet raysis obviated. Alternately, commercially available inexpensive lasers maybe used as the light source for the photopolymerization reaction.

The dental compositions according to the present invention may alsooptionally include pigments, opacifiers, brightening agents, handlingagents and other modificants.

The method of using the inventive dental adhesives and compositionsfollows, to an extent, the method currently practiced by those skilledin the art. The dental surface to be repaired is cleansed of decayedmaterial and is acid etched to promote bonding. At this point, a bondingagent may be employed by coating it upon the surface to be repaired. Thematerial of the present invention, including inert dental filler, isthen applied to the dental surface and molded to the surface accordingto conventional practices. The dental surface, including adhesive, isthen exposed to visible light from a light source and the presence ofthe ionic dye-counter ion complex generates free radicals which initiatefree radical polymerization or crosslinking of the acrylate basedadhesive material and subsequently cures the adhesive material. Whenused in this manner, the inventive composition functions both as anadhesive and as a dental restoration material.

Alternatively, the composition of the present invention may functionsolely as an adhesive. When used in this capacity, the dental surface iscleansed and the inventive adhesive is thereafter applied to thesurface. Dental restoration material is then applied onto the adhesivematerial and the dental surface is exposed to visible light to adherethe restoration material to the dental surface. When used in thisconfiguration, the restoration material should be transparent to enablelight waves to pass through said restoration material and contact theadhesive to initiate photopolymerization.

Obtaining a desired color for the adhesive can be controlled by the timelength of exposure to actinic radiation. Prolonged exposure to the lightsource will bleach the photoinitiator, thereby preventing unusualdiscoloration. Alternatively, if the retention of color is desired forcosmetic purposes, a lesser exposure time should be utilized.

The inventive photosensitive materials described herein also may beutilized in the field of photopolymer holography. A system known in theart contains a binder, photopolymerizable monomer, and photoinitiatorcoated onto a substrate as a film. The photoinitiator is selected toinitiate polymerization of the monomer at a selected wavelength.

A typical representative photopolymer holographic system consists of aphotopolymerizable monomer (40-50%), a cellulose acrylate butyratebinder (50-60%), and a bisimidazole initiator system (2-8%) sensitizedto 488 nm. The photopolymerizable monomer is typically an acrylate. Forexample, the monomer may be triethyleneglycol diacrylate, triethyleneglycol dimethacrylate, diethylene glycol diacrylate, decanedioldiacrylate, or trimethylolpropane triacrylate.

In operation, the film made up of the above mentioned constituents iscoated onto a substrate. Thereafter, the substrate is selectivelyilluminated with radiant light emitted from a laser in a predeterminedpattern to create a desired image pattern. Images are created in theregions that have become depleted in monomer due to photopolymerization.Thereafter, the image is "fixed" by either removing the remainingmonomer with an appropriate solution, or by a second, overall exposureto radiation.

In a typical embodiment, the initiator is selected to work incombination with a blue or ultraviolet light emitting laser source. Theuse of such a system is problematical in that the efficiency of theinitiator is low, and the cost of the laser is high.

In the present invention, by utilizing a cationic dye-borate anioncomplex, the photoinitiator is capable of initiating photopolymerizationwhen exposed to visible wavelengths. More specifically, when theinitiator is designed to be sensitive to red or green light, the use ofred or green lasers, respectively, to form the image may be utilized.This significantly decreases costs, as red and green light lasers aremuch more inexpensive than blue or ultraviolet light lasers.

In order to enhance the speed of the system, an autooxidant, such asN,N-dimethyl-2,6-diisopropylaniline may be included in the formulation.Further, optional thiols such as 2-mercaptobenzoxazole or6-ethoxy-2-mercaptobenzothiazole, may also be utilized in the system.

It is further envisioned that additional discrimination and resolutionmay be obtained by using at least two different inventivephotoinitiators which are sensitive to at least two differentwavelengths of light emitted by lasers. In such a system, at least twolasers emitting light at wavelengths corresponding to the sensitivitiesof the initiators selected would be used.

An additional use of the inventive photoinitiators of the presentinvention is their ability to be combined with ultraviolet absorbers inphotopolymerizable compounds to realize the twofold benefit ofphotopolymerization without corresponding ultraviolet degradation.

Many colored compounds are susceptible to degradation by ultravioletradiation. What typically occurs is that the compounds, upon exposure toultraviolet radiation, lose their true color and/or yellow. To combatthe discoloring of the compounds, it is common for ultravioletprotectants to be added to the composition. The protectants typicallytake the form of an ultraviolet absorber.

Examples of protectants known and used in the art are:2(3',5'-di-t-butyl-2'-hydroxy-phenyl)-5-chlorobenzotriazole,2(3'-t-butyl-5'-methyl-2'-hydroxyphenyl)-5-chlorobenzotriazole,2(2'-hydroxy-5'-met benzotriazole,2-(2-hydroxy-5-t-octylphenyl)-benzotriazole,2-hydroxy-4-n-octoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone,2-hydroxy-4-methoxybenzophenone, 4-dodecyloxy-2-hydroxybenzo-phenone,and 2-ethoxyethyl p-methoxycinnamate.

Although the above-mentioned protectants succeed in their radiationprotective function, when incorporated with photopolymerizablecompositions containing ultraviolet absorbing photoinitiators, theprotectants mask the function of the photoinitiators. As a result,photopolymerization cannot occur.

The inventors have discovered that the inventive cationic dye-borateanion compounds can be utilized in photopolymerizable compoundscontaining any of the above listed protectants. As the photoinitiatorsaccording to the present invention are sensitive to radiation in thevisible spectrum, typically red light and green light,photopolymerization can proceed while in the presence of the ultravioletprotectants. Accordingly, compounds can be produced which are capable ofphotopolymerizing and are not susceptible to ultraviolet degradation.Such compounds may be used in house paints, automobile paints,autobodies and accessories, road signs, windows, plastic piping andpolymeric parts used for supra-atmospheric applications.

EXAMPLE 3

Four photosensitive compositions were formulated. Two of thecompositions contained photoinitiators which were capable of generatingfree radicals upon exposure to ultraviolet radiation, one of thecompositions contained a photoinitiator sensitive to green light, andone of the compositions contained a photoinitiator sensitive to redlight. Each of the four compositions contained2(-2'-hydroxy-5'-methylphenyl) benzotriazole, a commercial ultravioletphotoprotectant sold under the name of Tinuvin P by Ciba Geigy. Theformulations were as follows:

    ______________________________________                                        Formulation A                                                                 TMPTA                   50    grams                                           Tinuvin P               5     grams                                           Irgacure 907 (UV initiator)                                                                           12    grams                                           Formulation B                                                                 TMPTA                   50    grams                                           Tinuvin P               5     grams                                           Quanticure ITX (UV initiator)                                                                         1     gram                                            2,6-diisopropyl-        1     gram                                            N,N-dimethylaniline (DIDMA)                                                   Formulation C (λmax = 548 nm)                                          TMPTA                   50    grams                                           Tinuvin P               5     grams                                           DIDMA                   1     gram                                            1,1'-di-n-heptyl-3,3,3',3'-                                                                           0.3   grams                                           tetramethylindocarbocyaninetetra-                                             phenylbutylborate                                                             Formulation D (λmax = 645 nm)                                          TMPTA                   50    grams                                           Tinuvin P               5     grams                                           DIDMA                   1     gram                                            1,1'-di-n-heptyl-3,3,3',3'-                                                                           0.4   grams                                           tetramethylindodicarbocyanine                                                 triphenyl-n-butylborate                                                       ______________________________________                                    

One drop of each of the above formulations was placed between glassslides and exposed to radiation emitted from one General ElectricF1518-CW fluorescent tube at a distance of 10 cm. The times fornoticeable polymerization and total slide immobilization are shown inTable 3.

                  TABLE 3                                                         ______________________________________                                        Formulation                                                                            Polymerization Time                                                                          Slide Immobilization Time                             ______________________________________                                        A        greater than 120 sec.                                                                        greater than 120 sec.                                 B        greater than 120 sec.                                                                        greater than 120 sec.                                 C        10 sec.        17 sec.                                               D        15 sec.        24 sec.                                               ______________________________________                                    

EXAMPLE 4

Formulations A, B, C and D of Example 3 were coated onto separate 5 milpolyethylene terephthalate strips by using a #18 Meyer bar. Strips ofeach coating were placed in a glass-covered frame and the frame wasflushed with argon for 10 minutes. The tubes were then exposed toradiation from two General Electric F1518-CW fluorescent tubes at adistance of 20 centimeters for 30 seconds. The cover of the frame wasremoved and the sample strips were inspected. Formulation A exhibited noapparent photopolymerization. Formulation B showed a slight amount ofphotopolymerization, but the strip was very tacky. Formulations C and Dhad cured to hard films, demonstrating that photopolymerization wascomplete.

A further use of the inventive photoinitiators is their ability to aidin the formulation of three dimensional models using computer controlledlasers. In current practice three dimensional models have been preparedby utilizing ultraviolet radiation generated from a computer controlledlaser to contact a solution containing a photopolymerizable composition.

The operation of such a system begins with the use of a computer withattached monitor to produce a two-dimensional or syntheticthree-dimensional image by using commonly available software programs.The computer is then interfaced separately to an ultraviolet laser andto a movable piston. The piston is located in a solution containing aphotopolymerizable monomer and an ultraviolet sensitive photoinitiator,and the piston is capable of upward and downward movement within thesolution, the movement of the piston being effectuated by the computer.Mounted onto the piston at its upper surface is a base which holds themodel to be formed. The laser is in optical contact with the solution.

Once all of the components are connected the model is produced by the"tracing" of the two-dimensional monitor to transfer its image to thesolution to form a three-dimensional model on a line by the line basis.By use of the computer, whether an image is to be transferred from agiven line to the solution is determined by whether the laser isactivated. If an image is to be produced for a given line, the laser isactuated by the computer to selectively expose the solution toultraviolet radiation to initiate photopolymerization via thephotoinitiator and to polymerize the exposed areas, causing these areasto harden. After tracing has been completed for a given line, theprocedure is repeated for the next line and the piston raises or lowersthe base appropriately to correspond to the shift in lines. Thisprocedure is completed until all lines have been traced and the completemodel has been produced. The model is then removed from the base.

Although the use of such a system provides an attractive alternative tomanual model formulation, the system suffers in that it requires the useof ultraviolet lasers and ultraviolet sensitive photoinitiators. The useof ultraviolet lasers is undesirable because such lasers are expensive,typically have a short lifetime, and have optical systems which are notcompletely reliable.

The inventors have discovered that if visible light-sensitivephotoinitiators capable of absorbing radiation in the visible spectrumand producing free radicals which initiate free radical polymerizationor crosslinking, and monomers which are free radical additionphotopolymerizable or crosslinkable are used in the model producingbath, the requirement of using ultraviolet lasers is obviated asphotopolymerization can occur by exposure of the bath to visible light.Preferred photoinitiators are cationic dye-borate anion compoundssensitive to either red or green light. By using these initiators, thewavelength emitted by the laser used for polymerizing the solution wouldcorrespond to the sensitivity of the photoinitiator. The use of visiblelight lasers provides the two-fold benefit of lowering costs of thesystem and improving the quality of the model produced due to thesuperior and more reliable optical qualities of the laser used.

In an additional embodiment, if it is desired to create a model havingmultiple colors, the above procedure can be repeated using multiplebaths corresponding to the numbers of colors desired. Each bath wouldcontain a polymerizable monomer and a photoinitiator having asensitivity corresponding to the color of light emitted by the laseracting upon the solution. Tracing would be repeated in each bath untilthe final object, having multiple colors, is produced.

It is envisioned that the model formulation system may be used tofabricate models for producing automobile parts, hardware, or any othermechanical parts capable of being generated by computer design.

The photosensitive compositions of the present invention are also usefulin coating surfaces under water. There has long been a need for systemsto control corrosion and biological fouling on underwater surfaces. Thefirst underwater-applicable coatings were viscous epoxy-polyamidematerials. These materials were applied by hand and cured slowly attemperatures below 60° F. (16° C.). Until cured, the coatings weresusceptible to wave damage.

Methods for repairing concrete offshore structures underwater have alsobeen desired. Techniques for the underwater placement of concrete havebeen available, however, the properties of the repaired structure do notcompare favorably with the original structure which was cast abovewater. Polymer concretes such as polyethylene oxide have found use inthis area. The repair must protect the steel reinforcement and preventits corrosion and restore and preferably increase the strength of thestructure.

A system for applying protective coatings to underwater surfaces andwhich permits damage or weathered coatings to be repaired on fixed orfloating structures has long been sought. Radiation curable compositionsare particularly desirable for such applications because they can be setrapidly and therefore are less susceptible to damage.

It has been found that the light sensitive compositions of the presentinvention can be fully cured under water. For use in underwaterapplications, the compositions are preferably prepared using waterinsoluble monomers. Particularly preferred monomers are acrylates andsome urethanes, those which can be free radical polymerized. Inaddition, the compositions may be modified to include corrosioninhibitors, biocides and/or wetting agents such as fatty acids, waxesand oils to enhance the compositions ability to wet immersed surfacesand displace surface water.

In most applications it will be desirable to carry out some form ofsurface preparation such as abrasive blasting, water blasting, wirebrushing, or the like to remove loose debris and any underwater growthas well as to roughen the surface and thereby improve adhesion.

One example of a formulation designed for underwater applicationcontains 0.2 wt.% of a cyanine borate photoinitiator, 3.8 wt.%pentamethylaniline, 96.0 wt.% TMPTA. Though this mixture cures brittle,it does polymerize. A better composition would be one which includes acopolymer to better enhance the properties of the film.

Having described the invention in detail and by reference to preferredembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims.

What is claimed is:
 1. A photohardenable composition comprising a freeradical addition polymerizable or crosslinkable compound, an ionicdye-reactive counter ion compound and a thiol, said ionic dye-reactivecounter ion compound being capable of absorbing actinic radiation andproducing free radicals which initiate free radical polymerization orcrosslinking of said polymerizable or crosslinkable compound and being astable non-transient compound prior to exposure to said actinicradiation.
 2. The photohardenable composition of claim 1 wherein saidcompound is an anionic dye compound.
 3. The composition according toclaim 2 wherein said thiol is selected from the group consisting ofmercaptobenzoxazoles, mercaptotetrazines and mercaptotriazines.
 4. Thecomposition according to claim 3 wherein said thiol is selected from thegroup consisting of 2-mercaptobenzothiazole,6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzoxazole,4-methyl-4H-1,2,4-triazole-3-thiol, 2-mercapto-1-methylimidazole,2-mercapto-5-methylthio-1,3,4-thiadiazole,5-n-butylthio-2-mercapto-1,3,4-thiadiazole, 4-methoxybenzenethiol,1-phenyl-1H-tetrazole-5-thiol, 4-phenyl-4H-1,2,4-triazole-3-thiol,2-mercaptobenzimidazole, pentaerythritol tetrakis(mercaptoacetate),pentaerythritol tetrakis(3-mercaptoproprionate), trimethylolpropane tris(mercapto-acetate), trimethylolpropane tris (3-mercaptopropionate),4-acetamidothiophenol, mercaptosuccinic acid, dodecanethiol,2-mercaptopyridine, 4-mercaptopyridine, 2-mercapto-3H-quinazoline, and2-mercaptothiazoline.
 5. The photohardenable composition of claim 1wherein said ionic dye-reactive counter ion compound is a cationicdye-borate anion complex.
 6. The photohardenable composition of claim 5wherein said cationic dye-borate anion complex is represented by theformula (I): ##STR36## where D is a cationic dye moiety; and R¹, R², R³and R⁴ are the same or different and selected from the group consistingof alkyl, aryl, aralkyl, alkaryl, alkenyl, alkynyl, alicyclic,heterocyclic, and allyl groups.
 7. The photohardenable composition ofclaim 6 wherein at least one of R¹, R², R³ and R⁴ is an alkyl group. 8.The photohardenable composition of claim 7 wherein said cationic dye isselected from the group consisting of cationic cyanine, carbocyanine,hemicyanine, rhodamine, and azamethine dyes.
 9. The compositionaccording to claim 5 wherein said thiol is a thiol selected from thegroup consisting of mercaptobenzoxazoles, mercaptotetrazines andmercaptotriazines.
 10. The composition according to claim 9 wherein saidthiol is selected from the group consisting of 2-mercaptobenzothiazole,6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzoxazole,4-methyl-4H-1,2,4-triazole-3-thiol, 2-mercapto-1-methylimidazole,2-mercapto-5-methylthio-1,3,4-thiadiazole,5-n-butylthio-2-mercapto-1,3,4-thiadiazole, 4-methoxybenzenethiol,1-phenyl-1H-tetrazole-5-thiol, 4-phenyl-4H-1,2,4-triazole-3-thiol,2-mercaptobenzimidazole, pentaerythritol tetrakis(mercaptoacetate),pentaerythritol tetrakis(3-mercaptoproprionate), trimethylolpropane tris(mercapto-acetate), trimethylolpropane tris (3-mercaptopropionate),4-acetamidothiophenol, mercaptosuccinic acid, dodecanethiol,2-mercaptopyridine, 4-mercaptopyridine, 2-mercapto-3H-quinazoline, and2-mercaptothiazoline.
 11. A photosensitive material comprising a supporthaving a layer of a photohardenable composition on the surface thereof,said composition comprising a free radical addition polymerizable orcrosslinkable compound, an ionic dye-reactive counter ion compound and athiol, said ionic dye-reactive counter ion compound being capable ofabsorbing actinic radiation and producing free radicals which initiatefree radical polymerization or crosslinking of said polymerizable orcrosslinkable compound and being a stable non-transient compound priorto exposure to said actinic radiation.
 12. The photosensitive materialof claim 11 wherein said complex is an anionic dye complex.
 13. Thephotosensitive material according to claim 12 wherein said thiol is athiol selected from the group consisting of mercaptobenzoxazoles,mercaptotetrazines and mercaptotriazines.
 14. The photosensitivematerial according to claim 13 wherein said thiol is selected from thegroup consisting of 2-mercaptobenzothiazole,6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzoxazole,4-methyl-4H-1,2,4-triazole-3-thiol, 2-mercapto-1-methylimidazole,2-mercapto-5-methylthio-1,3,4-thiadiazole,5-n-butylthio-2-mercapto-1,3,4-thiadiazole, 4-methoxybenzenethiol,1-phenyl-1H-tetrazole-5-thiol, 4-phenyl-4H-1,2,4-triazole-3-thiol,2-mercaptobenzimidazole, pentaerythritol tetrakis(mercaptoacetate),pentaerythritol tetrakis(3-mercaptoproprionate), trimethylolpropane tris(mercapto-acetate), trimethylolpropane tris (3-mercaptopropionate),4-acetamidothiophenol, mercaptosuccinic acid, dodecanethiol,2-mercaptopyridine, 4-mercaptopyridine, 2-mercapto-3H-quinazoline, and2-mercaptothiazoline.
 15. The photosensitive material of claim 11wherein said ionic dye-reactive counter ion compound is a cationicdye-borate anion complex.
 16. The photosensitive material of claim 15wherein said cationic dye-borate anion complex is represented by theformula (I) ##STR37## where D is a cationic dye moiety; and R¹, R², andR³ and R⁴ are the same or different and selected from the groupconsisting of alkyl, aryl, aralkyl, alkaryl, alkenyl, alkynyl,alicyclic, heterocyclic, and allyl groups.
 17. The photosensitivematerial of claim 16 wherein at least one of R¹, R², R³ and R⁴ is analkyl group and at least one is an aryl group.
 18. The photosensitivematerial of claim 17 wherein said cationic dye is selected from thegroup consisting of cationic cyanine, carbocyanine, hemicyanine,rhodamine, and azamethine dyes.
 19. The composition according to claim15 wherein said thiol is a thiol selected from the group consisting ofmercaptobenzoxazoles, mercaptotetrazines and mercaptotriazines.
 20. Thecomposition according to claim 19 wherein said thiol is selected fromthe group consisting of 2-mercaptobenzothiazole,6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzoxazole,4-methyl-4H-1,2,4-triazole-3-thiol, 2-mercapto-1-methylimidazole,2-mercapto-5-methylthio-1,3,4-thiadiazole,5-n-butylthio-2-mercapto-1,3,4-thiadiazole, 4-methoxybenzenethiol,1-phenyl-1H-tetrazole-5-thiol, 4-phenyl-4H-1,2,4-triazole-3-thiol,2-mercaptobenzimidazole, pentaerythritol tetrakis(mercaptoacetate),pentaerythritol tetrakis(3-mercaptoproprionate), trimethylolpropane tris(mercapto-acetate), trimethylolpropane tris (3-mercaptopropionate),4-acetamidothiophenol, mercaptosuccinic acid, dodecanethiol,2-mercaptopyridine, 4-mercaptopyridine, 2-mercapto-3H-quinazoline, and2-mercaptothiazoline.
 21. The photosensitive material of claim 12wherein said photohardenable composition is microencapsulated.
 22. Thephotosensitive material of claim 15 wherein said photohardenablecomposition is microencapsulated.
 23. The photosensitive material ofclaim 21 wherein said material is useful in forming full color imagesand said microcapsules include a first set of microcapsules having acyan image-forming agent associated therewith, a second set ofmicrocapsules having a magenta image-forming agent associated therewithand a third set of microcapsules having a yellow image-forming agentassociated therewith, at least one of said first, second and third setsof microcapsules containing said photohardenable composition containsaid ionic dye-counter ion compound.
 24. The photosensitive material ofclaim 22 wherein said material is useful in forming full color imagesand said microcapsules include a first set of microcapsules having acyan image-forming agent associated therewith, a second set ofmicrocapsules having a magenta image-forming agent associated therewithand a third set of microcapsules having a yellow image-forming agentassociated therewith, at least one of said first, second and third setsof microcapsules containing said photohardenable composition containsaid ionic dye-counter ion compound.